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  1. #1

    1/5 or 1/4 scale differential for homebuild with 49cc engine

    hello forum, recently i have been getting some ideas together of making an rc petrol buggy. currently i have an engine that i will use which is a 49cc 2stroke engine and have got it running. but i just dont know how to go about getting a differential and what ratios they are. i am wanting it to be pretty fast (45mph at least) and i want it to have a drive shaft input. any ideas would be helpful. thanks

  2. #2
    Lars from Norway's Avatar
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    Hello, you! I think i will start by directing you to this thread: Large scale home build projects - List of topics for you to take a look at all the threads there. Do you have any ideas on how to make the frame and setup of the car exept from what you have alread planned?
    Find a job you love, then you won\'\'t have to work for the rest of your life.

  3. #3
    Currently I am just in the planning stage and thought I should first get an engine,gearing and differential set up and have roughly the right gearing ratios first before I start trying to design a frame to go around parts I don't have yet. But should be just a flat sheet of metal with a engines mounted so the driveshaft would go Into the diff rather that having a chain driven one. And should from that be able to use some dogbones to the wheels and have independent suspension. Ohh and thanks for the link to that thread

  4. #4
    Ohh just thot of another alternative.maybe I could use a centre diff as a rear diff and have a chain coming from engine to a sprocket far back on the buggy then on that same shaft have a smaller cog that meshes with the centre(but now rear)diff. Just an idea. Might take a picture of that rough idea and the other one so u can get a better idea of what I mean

  5. #5
    Lars from Norway's Avatar
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    I understand, the latter option you mention here is exactly ( if i understand you correctly) the same as i have made on two of my cars. But i think it will be hard to get a bevel diffgear and pinion that will get the gearing low enough to make it work with a driveshaft directly from the clutch and to the diffgear.
    Find a job you love, then you won\'\'t have to work for the rest of your life.

  6. #6
    Well on the minimoto I got the engine from it had an 8t drive sprocket and a 50ish t rear sprocket which gives roughy a 6:1 drive ratio. I was thinking that I should maybe half it and go for a 3:1ish as the won't be thee weight of the driver so maybe a 13t pinion bevel gear and a 43t diff gear. Maybe that would be optimal torque to speed ratio. Still nothing certain though might get a few bevel pinions and try them out. Thanks for the help though

  7. #7
    Lars from Norway's Avatar
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    The 23 ccm engines on stock 1/5 cars has about 6:1 gearing, but 3:1, even if it is a 49 ccm engine, would be too much i think. I don't know the top rpm on your engine, but i think it will get a uncontrollable top speed with lack of torque. When i was constructing my first car i used a 36 ccm chainsaw-engine and 3:1-gearing, this made the clutchbell turn blue and the clutch shoes to glaze, and the theoretical top speed would end up at about 130 km per hour. I am older and wiser now
    Find a job you love, then you won\'\'t have to work for the rest of your life.

  8. #8
    Quote Originally Posted by Lars from Norway View Post
    The 23 ccm engines on stock 1/5 cars has about 6:1 gearing, but 3:1, even if it is a 49 ccm engine, would be too much i think. I don't know the top rpm on your engine, but i think it will get a uncontrollable top speed with lack of torque. When i was constructing my first car i used a 36 ccm chainsaw-engine and 3:1-gearing, this made the clutchbell turn blue and the clutch shoes to glaze, and the theoretical top speed would end up at about 130 km per hour. I am older and wiser now
    ohh, what ratio would you recommend for this. maybe an 8;1 or 10/1? and also i was wondering if you had any ideas for a differential? been searching for a while and haven't found anything suitable for such an engine. the only thing i can think of is a baja diff but that doesnt have a beveled gear on it for a drive shaft and bevel gear to give it power. or even if a bought diff isnt an option is it possible to build my own?

  9. #9
    Lars from Norway's Avatar
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    About 6:1 would be nice to try with first, maybe you can go down to 5:1 if it feels like it has enough power for it.
    Yes, you can build a diff, but it takes a lot of work, machining, spinning with lathe, milling and lots of other operations. It would be easier to get a Baja-diff and gear it down 3 or 4:1 with pinion and diff-gear, and take the rest by gearing it down 3 or 2:1 by using the bevel gear to connect to the clutch with an axle.
    Find a job you love, then you won\'\'t have to work for the rest of your life.

  10. #10
    Quote Originally Posted by Lars from Norway View Post
    About 6:1 would be nice to try with first, maybe you can go down to 5:1 if it feels like it has enough power for it.
    Yes, you can build a diff, but it takes a lot of work, machining, spinning with lathe, milling and lots of other operations. It would be easier to get a Baja-diff and gear it down 3 or 4:1 with pinion and diff-gear, and take the rest by gearing it down 3 or 2:1 by using the bevel gear to connect to the clutch with an axle.
    Ok thanks for the help, managed to order a diff went with something similar size size to a Baja diff, the maverick blackout diff, as it was half the price and it was fully assembled with input cups, bearings and full casing. Will follow ur advise on the ratio and go for 6:1 as a starting point. U have been a great help in this project.. Cheers

  11. #11
    Lars from Norway's Avatar
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    Nice to help, i am ready for more
    Find a job you love, then you won\'\'t have to work for the rest of your life.


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